1. Field of the Invention
The present invention relates to a mutual-capacitance, projected-capacitive touch screen device that determines whether or not a touch is present based on an amount of change in a charge-discharge current at each intersection of electrodes arranged in a grid pattern, and a method of producing the touch screen device.
2. Description of Related Art
There are various types of touch screen devices. A capacitive touch screen device does not require an electronic pen including an oscillator or the like, and a touch operation on the capacitive touch screen device can be performed directly with a finger tip of a user or with a stylus simply made of a conductive material.
A projected capacitive touch screen device includes first electrodes and second electrodes arranged in a grid pattern, and uses a principle that capacitance of a capacitor provided at each intersection (hereinafter, referred to as an electrode intersection) of the first electrodes and the second electrodes varies with a close access or a contact of a conductive object (e.g., human body). A mutual-capacitance, projected-capacitive touch screen device detects whether a touch is present based on an amount of change in the charge-discharge current according to the change in capacitance at each electrode intersection, It is possible to perform multi-touch (or multipoint detection), which detects a plurality of touch positions simultaneously, in the mutual-capacitance, projected-capacitive touch screen device.
The projected capacitive touch screen device has a protective layer in which the first electrodes and the second electrodes are implanted, and a surface board with a touch surface is provided on a front surface side of the protective layer (see Related Arts 1 and 2).
The touch screen device is widely used in fields of personal computers or handheld terminals. On the other hand, a technology is known in which the touch screen device is used as an interactive whiteboard, by combining the touch screen device with a large screen display device to be used in a presentation or a lecture for a large audience (see Related Art 3).
Related Art 1: Japanese Patent Application Publication No. 2002-342033    Related Art 2: U.S. Pat. No. 4,686,332    Related Art 3: Japanese Patent Application Publication No. 2009-86855
When the mutual-capacitance, projected-capacitive touch screen device is used as an interactive whiteboard, overall capacitance between the first electrodes and the second electrodes increases, as the size of the touch screen device increases. For example, the capacitance exceeds 100 pF in the device having a 77 inch screen. On the other hand, the change in capacitance in accordance with a touch operation by a user's finger tip or a stylus is at most several 100 fF, and thus is very small. Accordingly, as the size of the touch screen device increases, a sufficient detection accuracy cannot be obtained.